Conventionally, a monostable electromagnetic actuator as shown in FIG. 6 and a bistable electromagnetic actuator as shown in FIG. 7 have been commonly used. The monostable type shown in FIG. 6 comprises stationary element 1 made of soft magnetic material, permanent magnet 3 the magnetic pole S of which is secured to the stationary element 1, movable element 2 made of soft magnetic material, and electromagnetic coil 4 arranged in the stationary element 1. One end of the movable element 2 is connected to a spring 5 so as to apply bias force to the movable element 2. FIG. 6 shows one mechanical stable state that a magnetic pole 1a of the stationary element 1 and another magnetic pole 2a of the movable element 2 are magnetically attracted to each other against the bias force of the spring 5 due to magnetic flux 14 caused by the permanent magnet 3. When electric current in a pulse series is so flowed through the electromagnetic coil 4 as to generate magnetic flux 15 in the counter direction of the magnetic flux 14 caused by the permanent magnet 3, the magnetic attractive force between the stationary element 1 and the movable element 2 is cancelled and thus the movable element 2 is moved by the bias force of the spring 5.
FIG. 7 shows also one mechanical stable state of the other actuator wherein a movable element 2 made of soft magnetic material is magnetically attracted to one end of a stationary element 1 made of soft magnetic material. That is, a permanent magnet 3 is arranged in the stationary element 1 so that magnetic pole S of the magnet 3 is secured to the inner surface of the element 1. The magnet 3 generates magnetic flux 14 which makes first magnetic pole 2a of the movable element 2 to contact the first magnetic pole 1a of the stationary element 1. When electric current in a pulse series is flowed through a first coil 4a windingly disposed in the stationary element 1 so as to generate magnetic flux 15 in the counter direction of the magnetic flux 14 caused by the permanent magnet 3, the movable element 2 is moved rightward in the drawing and thus second magnetic pole 2b of the movable element 2 is magnetically contacted to second magnetic pole 1b of the stationary element 1; this is another mechanical stable state.
In order to return this actuator to the initial stable condition, electric current in a pulse series is flowed through second coil 4b in the reverse direction of the above.
However, as can be clear from the aforementioned explanation, these conventional electromagnetic actuators have the following demerits.
(1) The electromagnetic actuator requires long value of ampere turn required for the coil in order to switch the mechanical stable state to another because the permanent magnet being arranged in the magnetic circuit which gererates magnetomotive force caused by the flow of the current through the coil and having large magnetic reluctance is required.
(2) The monostable electromagnetic actuator requires mechanical bias force caused by a spring or the like, so that its constitution becomes complicated.
(3) The electromagnetic actuator requires a particular permanent magnet having so strong magnetomotive force as to maintain the mechanical stable condition.
(4) The bistable electromagnetic actuator does not always require means for generating mechanical bias force such as a spring, but it requires two coils capable of generating so large magnetomotive force as to move the movable element. This causes a large sized and complicated device.